Latest content added for UNT Digital Library Partner: UNT Librarieshttp://digital.library.unt.edu/explore/partners/UNT/browse/?fq=str_degree_discipline:Physics&start=40&fq=untl_collection:UNTETD2013-03-04T14:02:27-06:00UNT LibrariesThis is a custom feed for browsing UNT Digital Library Partner: UNT LibrariesA Non-equilibrium Approach to Scale Free Networks2013-03-04T14:02:27-06:00http://digital.library.unt.edu/ark:/67531/metadc149609/<p><a href="/ark:/67531/metadc149609/"><img alt="A Non-equilibrium Approach to Scale Free Networks" title="A Non-equilibrium Approach to Scale Free Networks" src="/ark:/67531/metadc149609/thumbnail/"/></a></p><p>Many processes and systems in nature and society can be characterized as large numbers of discrete elements that are (usually non-uniformly) interrelated. These networks were long thought to be random, but in the late 1990s, Barabási and Albert found that an underlying structure did in fact exist in many natural and technological networks that are now referred to as scale free. Since then, researchers have gained a much deeper understanding of this particular form of complexity, largely by combining graph theory, statistical physics, and advances in computing technology. This dissertation focuses on out-of-equilibrium dynamic processes as they unfold on these complex networks. Diffusion in networks of non-interacting nodes is shown to be temporally complex, while equilibrium is represented by a stable state with Poissonian fluctuations. Scale free networks achieve equilibrium very quickly compared to regular networks, and the most efficient are those with the lowest inverse power law exponent. Temporally complex diffusion also occurs in networks with interacting nodes under a cooperative decision-making model. At a critical value of the cooperation parameter, the most efficient scale free network achieves consensus almost as quickly as the equivalent all-to-all network. This finding suggests that the ubiquity of scale free networks in nature is due to Zipf's principle of least effort. It also suggests that an efficient scale free network structure may be optimal for real networks that require high connectivity but are hampered by high link costs.</p>Theoretical and Experimental Investigations Concerning Microgels of Varied Spherical Geometries2013-03-04T14:02:27-06:00http://digital.library.unt.edu/ark:/67531/metadc149680/<p><a href="/ark:/67531/metadc149680/"><img alt="Theoretical and Experimental Investigations Concerning Microgels of Varied Spherical Geometries" title="Theoretical and Experimental Investigations Concerning Microgels of Varied Spherical Geometries" src="/ark:/67531/metadc149680/thumbnail/"/></a></p><p>Polymer gels have been studied extensively due to their ability to simulate biological tissues and to swell or collapse reversibly in response to external stimuli. This work presents a variety of studies using poly-N-isopropylacrylamide (PNIPA) hydrogels. The projects have been carried out both in the lab of Dr. Zhibing Hu and in collaboration with others outside of UNT: (1) an analysis of the swelling kinetics of microgel spherical shells prepared using a novel design of microfluidic devices; (2) a comparison of the drug-release rates between nanoparticle structures having either core or core-with-shell (core-shell) designs; (3) an investigation into the thermodynamics of swelling for microgels of exceedingly small size.</p>Ultrafast Spectroscopy of Hybrid Ingan/gan Quantum Wells2013-03-04T14:02:27-06:00http://digital.library.unt.edu/ark:/67531/metadc149635/<p><a href="/ark:/67531/metadc149635/"><img alt="Ultrafast Spectroscopy of Hybrid Ingan/gan Quantum Wells" title="Ultrafast Spectroscopy of Hybrid Ingan/gan Quantum Wells" src="/ark:/67531/metadc149635/thumbnail/"/></a></p><p>Group III nitrides are efficient light emitters. The modification of internal optoelectronic properties of these materials due to strain, external or internal electric field are an area of interest. Insertion of metal nanoparticles (MNPs) (Ag, Au etc) inside the V-shaped inverted hexagonal pits (IHP) of InGaN/GaN quantum wells (QWs) offers the potential of improving the light emission efficiencies. We have observed redshift and blueshift due to the Au MNPs and Ag MNPs respectively. This shift could be due to the electric field created by the MNPs through electrostatic image charge. We have studied the ultrafast carrier dynamics of carriers in hybrid InGaN/GaN QWs. The change in quantum confinement stark effect due to MNPs plays an important role for slow and fast carrier dynamics. We have also observed the image charge effect on the ultrafast differential transmission measurement due to the MNPs. We have studied the non-linear absorption spectroscopy of these materials. The QWs behave as a discharging of a nanocapacitor for the screening of the piezoelectric field due to the photo-excited carriers. We have separated out screening and excitonic bleaching components from the main differential absorption spectra of InGaN/GaN QWs.</p>Variational Wave Function for Sodium2012-12-27T22:03:54-06:00http://digital.library.unt.edu/ark:/67531/metadc130344/<p><a href="/ark:/67531/metadc130344/"><img alt="Variational Wave Function for Sodium" title="Variational Wave Function for Sodium" src="/ark:/67531/metadc130344/thumbnail/"/></a></p><p>The practical method of applying the variation principle to the calculation of the energy of an atom demands a trial function which contains variable parameters. The previous work done using this approach was based on the use of some combination of hydrogenic wave functions containing parameters inserted in appropriate places. The present calculation of the energy of the eleven-electron atom has been brought about using this method.</p>Operation and Control of a Radiofrequency Ion Source2012-12-27T22:03:54-06:00http://digital.library.unt.edu/ark:/67531/metadc130340/<p><a href="/ark:/67531/metadc130340/"><img alt="Operation and Control of a Radiofrequency Ion Source" title="Operation and Control of a Radiofrequency Ion Source" src="/ark:/67531/metadc130340/thumbnail/"/></a></p><p>This thesis examines the operation and control of a radiofrequency ion source.</p>Neutron Density Depression Due to an Oblate Spheroidal Detector2012-12-27T22:03:54-06:00http://digital.library.unt.edu/ark:/67531/metadc130362/<p><a href="/ark:/67531/metadc130362/"><img alt="Neutron Density Depression Due to an Oblate Spheroidal Detector" title="Neutron Density Depression Due to an Oblate Spheroidal Detector" src="/ark:/67531/metadc130362/thumbnail/"/></a></p><p>In this paper, two projects have been undertaken. First, Workman's calculations have been checked to a higher degree of approximation to determine the accuracy of his method. Second, a new set of boundary conditions has been developed for obtaining solutions of the neutron diffusion equation which do not depend on the solution of the equation inside the detector.</p>Dynamical Friction Coefficients for Plasmas Exhibiting Non-Spherical Electron Velocity Distributions2012-12-27T22:03:54-06:00http://digital.library.unt.edu/ark:/67531/metadc130480/<p><a href="/ark:/67531/metadc130480/"><img alt="Dynamical Friction Coefficients for Plasmas Exhibiting Non-Spherical Electron Velocity Distributions" title="Dynamical Friction Coefficients for Plasmas Exhibiting Non-Spherical Electron Velocity Distributions" src="/ark:/67531/metadc130480/thumbnail/"/></a></p><p>This investigation is designed to find the net rate of decrease in the component of velocity parallel to the original direction of motion of a proton moving through an electron gas exhibiting a non-spherical velocity distribution.</p>Energy Losses of Protons Projected through a Plasma Due to Collisions with Electrons of the Plasma for a Variety of Non-Maxwellian Electron Velocity Distributions2012-12-27T22:03:54-06:00http://digital.library.unt.edu/ark:/67531/metadc130468/<p><a href="/ark:/67531/metadc130468/"><img alt="Energy Losses of Protons Projected through a Plasma Due to Collisions with Electrons of the Plasma for a Variety of Non-Maxwellian Electron Velocity Distributions" title="Energy Losses of Protons Projected through a Plasma Due to Collisions with Electrons of the Plasma for a Variety of Non-Maxwellian Electron Velocity Distributions" src="/ark:/67531/metadc130468/thumbnail/"/></a></p><p>The purpose of this thesis is to study energy losses suffered by protons in traversing a plasma through collision with the electrons of the plasma. For these electrons a variety of non-Maxwellian velocity distributions are assumed.</p>A Computer Analysis of Complex Gamma-Ray Spectra2012-12-27T22:03:54-06:00http://digital.library.unt.edu/ark:/67531/metadc130612/<p><a href="/ark:/67531/metadc130612/"><img alt="A Computer Analysis of Complex Gamma-Ray Spectra" title="A Computer Analysis of Complex Gamma-Ray Spectra" src="/ark:/67531/metadc130612/thumbnail/"/></a></p><p>The purpose of this investigation was to provide a method for determining the relative intensities of all gamma rays in a particular spectrum, and thereby determine the relative transition probabilities.</p>Electron Transport in Bismuth at Liquid Helium Tempratures2012-12-27T22:03:54-06:00http://digital.library.unt.edu/ark:/67531/metadc130512/<p><a href="/ark:/67531/metadc130512/"><img alt="Electron Transport in Bismuth at Liquid Helium Tempratures" title="Electron Transport in Bismuth at Liquid Helium Tempratures" src="/ark:/67531/metadc130512/thumbnail/"/></a></p><p>To obtain information on the band structure of bismuth, galvanomagnetic potentials were measured in a single crystal at liquid-helium and liquid-nitrogen temperatures. These measurements were analyzed for information on the different carriers, particularly for the existence of a high-mobility band of holes.</p>